Solid state imaging devices, including charge coupled devices (CCD), complementary metal oxide semiconductor (CMOS) imaging devices, and others, have been used in photo-imaging applications. A solid state imaging device circuit includes a focal plane array of pixel cells, or pixels, as an image sensor, each pixel includes a photosensor, which may be a photogate, photoconductor, a photodiode, or other photosensor having a doped region for accumulating photo-generated charge.
For CMOS imaging devices, each pixel has a charge storage region, formed over or in a substrate, which is connected to a gate of an output transistor, which is part of a readout circuit. The charge storage region can be constructed as a floating diffusion region. In some CMOS imaging devices, each pixel may further include at least one electronic device, such as a transistor, for transferring charge from the photosensor to the storage region and one device, also typically a transistor, for resetting the storage region to a predetermined charge level prior to charge transference. CMOS imaging devices of the type discussed above are discussed, for example, in U.S. Pat. No. 6,140,630, U.S. Pat. No. 6,376,868, U.S. Pat. No. 6,310,366, U.S. Pat. No. 6,326,652, U.S. Pat. No. 6,204,524, and U.S. Pat. No. 6,333,205, each assigned to Micron Technology, Inc. Imaging devices are typically incorporated into a larger device, such as a digital camera or other imaging apparatus, which may also include image processing and memory circuitry to provide an output image.
In digital photography, ISO, also called analog gain, denotes how sensitive the image sensor is to the amount of light present. The higher the ISO, the more sensitive the image sensor, enabling it to take pictures in low-light situations. A camera's ISO function sets the light sensitivity of the camera's image sensor (this is similar to the speed rating of film). ISO settings are often rated at 100, 200, or 400, often including intermediate values of these settings, but can go as high as 800, 1600, and even 3200 on some advanced camera models. A lower ISO setting is used when capturing overly bright scenes, since it reduces the light sensitivity of the image sensor. A higher ISO setting is often used when shooting under dimmer conditions (cloudy days, indoors, etc.) since it increases the light sensitivity of the image sensor. At lower ISO settings images are captured with larger exposure periods which captures more light, but which also increases the risk of motion blur.
A desired feature in all modern digital cameras, even low-end camera-on-chip models, is image stabilization, resulting in reduced image blurring. Image stabilization is the ability of the camera to avoid image smear of objects in the field of view, which can be caused by camera shaking or by movements of the objects themselves. Image stabilization is desirable particularly when longer exposure periods are used. One way image stabilization has been implemented is by increasing the analog gain applied to pixel signals, while correspondingly reducing exposure (integration) time. This results in less image smearing and sharper pictures. However, this reduction in exposure time can cause image noise to increase. Some current methods of image stabilization also rely on extra hardware in the camera.
An image device and method providing image stabilization, which may include camera movement sensing circuits, lens control devices, additional software processing and other components, that does not cause an unacceptable image noise increase, and which relies on existing image capture and processing software, is desirable.